Numerous applications are found for such toroidal rings in various fields. According to the type of use, several manufacturing methods have been implemented, such as screwing, conical fitting or even soldering. If the conditions of use are particularly severe, as is the case, for example, when the toroidal ring constitutes the inner core of a metal sealing ring having at least an outer sheath, known manufacturing methods are no longer suitable.
Indeed, screwing always leaves a residual gap breaking the continuity of the turns; after a great number of cycles of cyclic stresses such as dismantling and assembling, putting under pressure or under vacuum, raising and lowering of temperature, this gap allows plastic deformation which could impair sealing. The conical fitting has the same disadvantage, a residual gap being inevitably formed. Soldering would perhaps give better results, but it remains a very limited method suitable only for applications where temperature do not exceed approximately 120.degree. C.